Semiconductor device and manufacturing method thereof

ABSTRACT

A semiconductor device according to an embodiment includes: a barrier metal layer provided on a surface of an insulating layer; and a conductive layer having a first metal layer provided on a surface of the barrier metal layer, and a second metal layer provided on a surface of the first metal layer. The second metal layer includes an identical metal to metal of the first metal layer, and an impurity configured to remove fluorine bonded to the metal.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is based upon and claims the benefit of priority from Japanese Patent Application No. 2019-167191, filed on Sep. 13, 2019; the entire contents of which are incorporated herein by reference.

FIELD

Embodiments of the present invention relate to a semiconductor device and a manufacturing method thereof.

BACKGROUND

There are formed, in manufacturing of a semiconductor device, lines including contact plugs, via plugs, word lines and the like. For the formation of such lines, film formation technologies are used, such, for example, as CVD (Chemical Vapor Deposition) and ALD (Atomic Layer Deposition). In these film formation technologies, the lines are formed, for example, by alternately introducing material gas including fluorine and metal, such as tungsten hexafluoride (WF₆), and reducing gas including hydrogen (H₂).

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross sectional view showing a configuration of the essential part of a semiconductor device according to a first embodiment;

FIG. 2 is a cross sectional view having an electrode layer expanded;

FIG. 3 is a cross sectional view for explaining a step of forming a block insulating layer;

FIG. 4 is a cross sectional view for explaining a step of forming a barrier metal layer;

FIG. 5 is a cross sectional view for explaining a step of forming a metal layer;

FIG. 6 is a flowchart showing general manufacturing steps of a metal layer by ALD;

FIG. 7 is a cross sectional view having the essential part of a semiconductor device according to a second embodiment expanded; and

FIG. 8 is a flowchart showing manufacturing steps of the metal layer in a fifth embodiment.

DETAILED DESCRIPTION

Embodiments will now be explained with reference to the accompanying drawings. The present invention is not limited to the embodiments.

A semiconductor device according to an embodiment includes: a barrier metal layer provided on a surface of an insulating layer; and a conductive layer having a first metal layer provided on a surface of the barrier metal layer, and a second metal layer provided on a surface of the first metal layer. The second metal layer includes an identical metal to metal of the first metal layer, and an impurity configured to remove fluorine bonded to the metal.

While in the embodiments mentioned later, the present invention is applied to word lines of three-dimensionally stacked semiconductor memories, it can also be applied to lines other than word lines, such, for example, as contact plugs and via plugs. Moreover, it can also be applied to lines of semiconductor devices other than three-dimensionally stacked semiconductor memories.

First Embodiment

FIG. 1 is a cross sectional view showing a configuration of the essential part of a semiconductor device according to a first embodiment. A semiconductor device 1 shown in FIG. 1 includes a semiconductor substrate 10, a stacked body 20 and a memory film 30.

The semiconductor substrate 10 is exemplarily a silicon substrate. The stacked body 20 is provided on the semiconductor substrate.

As shown in FIG. 1, the stacked body 20 has a plurality of electrode layers 21 and a plurality of insulating layers 22. The plurality of electrode layers 21 and the plurality of insulating layers 22 are alternately stacked in a Z-direction perpendicular to the semiconductor substrate 10. The plurality of electrode layers 21 function as word lines of this three-dimensionally stacked semiconductor memory. The plurality of insulating layers 22 exemplarily includes silicon oxide (SiO₂), and insulatively separate the individual electrode layers 21.

FIG. 2 is a cross sectional view having the electrode layer 21 expanded. As shown in FIG. 2, the electrode layer 21 has a block insulating layer 211 (insulating layer), a barrier metal layer 212, a metal layer 213 (first metal layer) and a metal layer 214 (second metal layer). The metal layer 213 and the metal layer 214 constitute a conductive layer.

The block insulating layer 211 exemplarily includes aluminum oxide (Al₂O₃), and is provided on surfaces of the insulating layers 22. The barrier metal layer 212 exemplarily includes titanium nitride (TiN), and is provided on a surface of the block insulating layer 211. A thickness of the barrier metal layer 212 is approximately 3 nm.

The metal layer 213 is provided on a surface of the barrier metal layer 212. The metal layer 213 is an initial nucleation layer for metal, and includes a metal and a nucleation substance for improving a nucleation density of the metal. The metal is exemplarily tungsten (W). The nucleation substance is exemplarily diborane (B₂H₆) or monosilane (SiH₄). Moreover, a thickness of the metal layer 213 is not more than 5 nm.

The metal layer 214 is provided on a surface of the metal layer 213. The metal layer 214 is a bulk layer including an identical metal to metal of the metal layer 213 and an impurity capable of removing fluorine bonded to the metal contained in the metal layer 214. The metal is exemplarily tungsten (W). The impurity is exemplarily at least one of an aluminum atom (Al), a zirconium atom (Zr), a hafnium atom (Hf), a silicon atom (Si), a boron atom (B), a titanium atom (Ti), an oxygen atom (O), an yttrium atom (Y) and a carbon atom (C). A specific resistance of the metal layer 214 is desirably not more than 40 μΩ·cm. Notably, a bond energy between tungsten and each of the aforementioned atoms except the oxygen atom and the carbon atom among the aforementioned exemplary impurities is higher than a bond energy between tungsten and fluorine.

As shown in FIG. 1, the memory film 30 has a block insulating film 31, a charge storage film 32, a tunnel insulating film 33, a channel film 34 and a core insulating film 35. The block insulating film 31 exemplarily includes silicon oxide, and faces the electrode layers 21 and the insulating layers 22. The charge storage film 32 exemplarily includes silicon nitride (SiN), and faces an inner circumferential surface of the block insulating film 31. The tunnel insulating film 33 exemplarily includes silicon oxide nitride (SiON), and faces an inner circumferential surface of the charge storage film 32. The channel film 34 exemplarily includes polysilicon, and faces an inner circumferential surface of the tunnel insulating film 33. The core insulating film 35 exemplarily includes silicon oxide, and faces an inner circumferential surface of the channel film 34. Notably, the structure of the memory film 30 is not limited to the structure shown in FIG. 1.

Hereafter, manufacturing steps of the semiconductor device according to the present embodiment are described. Film formation steps for the electrode layers 21 are herein described.

First, as shown in FIG. 3, the block insulating layer 211 is formed on the surfaces of the insulating layers 22. Next, as shown in FIG. 4, the barrier metal layer 212 is formed on the surface of the block insulating layer 211.

Next, as shown in FIG. 5, the metal layer 213 is formed on the surface of the barrier metal layer 212. In the present embodiment, the metal layer 213 is formed in a chamber (not shown) in an ALD scheme. A temperature in the chamber is set to be 200 to 350° C. A pressure in the chamber is set to be 400 to 2000 Pa (3 to 15 Torr).

Under the conditions for the temperature and the pressure as set above, first, diborane gas or silane gas is introduced into the chamber. Next, inert gas such as argon gas is introduced into the chamber. Next, material gas such as tungsten hexafluoride gas is introduced into the chamber. After that, the inert gas is introduced again into the chamber. By repeating such introductions of gas, the metal layer 213 is formed, as an initial layer, on the surface of the barrier metal layer 212.

In the final stage, the metal layer 214 is formed, as a bulk layer, on the surface of the metal layer 213. In the present embodiment, the metal layer 214 is formed in a chamber (not shown) for ALD similarly to the metal layer 213.

FIG. 6 is a flowchart showing general manufacturing steps of a metal layer by ALD. In general, when a metal layer is formed by ALD, first, material gas such as tungsten hexafluoride gas is introduced into a chamber (step S11). Next, inert gas such as argon is introduced into the chamber (step S12). Next, reducing gas such as hydrogen gas is introduced into the chamber (step S13). Next, the inert gas is introduced again into the chamber (step S14).

After such cycles are repeated a predetermined number of times each of which cycles is composed of the aforementioned step S11 to step S14, the metal layer is formed. Meanwhile, when fluorine is contained in the material gas, some of the fluorine occasionally remains in the metal layer. This can cause a concern that the remaining fluorine results in failure such as leakage.

Therefore, in the present embodiment, an additive gas is newly introduced into the chamber in forming the metal layer 214. Since molecules of the additive gas include impurities capable of removing fluorine bonded to tungsten, the impurity results in bonding to tungsten, and a fluorine compound obtained through reaction of fluorine with another element contained in the additive gas is generated.

The impurity, which is contained in the additive gas, is at least one of an aluminum atom (Al), a zirconium atom (Zr), a hafnium atom (Hf), a silicon atom (Si), a boron atom (B), a titanium atom (Ti), an oxygen atom (O), an yttrium atom (Y) and a carbon atom (C) as mentioned above

When the impurity is the aluminum atom, the additive gas is desirably gas including TMA (trimethylaluminum) or aluminum chloride (AlCl₃), for example. When the impurity is the zirconium atom, the additive gas is desirably gas including zirconium chloride (ZrCl₄) or TDMAZ (tetrakis(dimethylamino)zirconium). When the impurity is the hafnium atom, the additive gas is desirably gas including hafnium chloride (HfCl₄) or TDMAH (tetrakis(dimethylamino)hafnium).

When the impurity is the silicon atom, the additive gas is desirably gas including monosilane (SiH₄), disilane (Si₂H₆), trisilane (Si₃H₈), monochlorosilane (SiH₃Cl), dichlorosilane (SiH₂Cl₂), hexachlorosilane (Si₂Cl₆), methylsilane (SiH₃CH₃) or dimethylsilane (SiH₂(CH₃)₂).

When the impurity is the boron atom, the additive gas is desirably gas including diborane or boron trichloride (BCl₃). When the impurity is the titanium atom, the additive gas is desirably gas including titanium tetrachloride (TiCl₄) or TDMAT (tetrakis(dimethylamino)titanium). When the impurity is the carbon atom or the oxygen atom, the additive gas is desirably gas including carbon monoxide (CO), carbon dioxide (CO₂), an oxygen molecule (O₂), nitrous oxide (N₂O) or nitric monoxide (NO).

When diborane gas among the aforementioned inert gases is used for forming the metal layer 214, the temperature (film formation temperature) in the chamber is desirably set to be approximately 200 to 400° C. because of high reactivity of diborane.

Moreover, if diborane gas were introduced simultaneously to the tungsten hexafluoride gas (material gas), diborane would result in its reaction with tungsten hexafluoride. Therefore, diborane gas is desirably introduced in different timing from that for the tungsten hexafluoride gas. For example, in order to restrain decomposition of diborane, the diborane gas is desirably introduced into the chamber simultaneously to the hydrogen gas (reducing gas) in step S13 mentioned above. This can control an amount of boron taken into the metal layer 214.

When monosilane gas is used for the inert gas, the temperature (film formation temperature) in the chamber can be set to be approximately 200 to 500° C. because of a higher decomposition temperature of monosilane than a decomposition temperature of diborane. Moreover, since monosilane is highly reactive with tungsten hexafluoride similarly to diborane, monosilane is desirably introduced in different timing from that for the tungsten hexafluoride gas. The monosilane gas is also desirably introduced simultaneously to the hydrogen gas in step S13 mentioned above similarly to diborane. This can control an amount of silicon taken into the metal layer 214.

When diborane gas and silane gas are used for the inert gas, if concentrations of boron and silicon taken into the metal layer 214 are high, a resistance of the metal layer 214 increases. Therefore, by adjusting flow rates, partial pressures, periods of introduction, and the like of the diborane gas and the silane gas, a boron concentration or a silicon concentration in the metal layer 214 is desirably set to be 1×10¹⁹ to 1×10²¹ atoms/cm³.

According to the present embodiment described above, since the additive gas is introduced for every cycle in forming the metal layer 214, the impurity is taken into the metal layer 214 so as to take a uniform concentration therein. Since in this stage, the impurity promotes cleavage of a bond between the metal (tungsten) of the metal layer 214 and fluorine, fluorine scarcely remains in the metal layer 214. Accordingly, failure originated from fluorine can be improved in a thermal process performed after formation of the electrode layers 21.

Second Embodiment

FIG. 7 is a cross sectional view having the essential part of a semiconductor device according to a second embodiment expanded. The similar components to those for the aforementioned first embodiment are given the same signs and their detailed description is omitted.

In a semiconductor device 2 according to the present embodiment, a structure of the metal layer 214 is different from that for the first embodiment. As shown in FIG. 7, the metal layer 214 has a high concentration layer 214 a in which the concentration of the impurity described for the first embodiment is locally high. Similarly to the first embodiment, the metal layer 214 is formed with an additive gas including the aforementioned impurity. The larger the amount of the impurity taken into the metal layer 214 is, the larger the resistance of the metal layer 214 becomes.

Therefore, in the present embodiment, after the cycle of gas introduction in step S11 to step S14 shown in FIG. 6 is repeated a predetermined number of times, the cycle in which the additive gas is introduced is performed, and thereby, the metal layer 214 is formed. For example, when the impurity is exemplarily diborane, every time when 250 cycles of introduction of the material gas including tungsten hexafluoride, introduction of the inert gas including argon, introduction of the reducing gas including hydrogen, and introduction of the inert gas including argon are performed, a cycle of the introduction of the aforementioned material gas, the introduction of the aforementioned inert gas, simultaneous introduction of diborane gas and the aforementioned reducing gas, and the introduction of the aforementioned inert gas is added. Thereby, there is formed, in the metal layer 214, at least one high concentration layer 214 a in which the diborane concentration is locally high.

According to the present embodiment described above, similarly to the first embodiment, fluorine scarcely remains in the metal layer 214 due to the impurity contained in the additive gas. Moreover, introduction of the additive gas is reduced to be as less as possible. Thereby, failure originated from fluorine can be reduced while the resistance of the metal layer 214 is reduced.

Third Embodiment

A third embodiment is hereafter described. Its differences from the first embodiment are herein mainly described. A formation method of the metal layer 214 in the present embodiment is different from that in the first embodiment.

In the present embodiment, the additive gas has a property of scarcely reacting with the material gas or the reducing gas. Therefore, the additive gas is continuously introduced throughout step S11 to step S14 shown in FIG. 6. Thereby, there can be sufficiently secured a time for taking the impurity contained in the additive gas into the metal layer 214, in other words, a time for removing fluorine from the metal layer 214. When the material gas includes tungsten hexafluoride and the reducing gas includes hydrogen, the additive gas includes titanium tetrachloride or dichlorosilane.

According to the present embodiment described above, the additive gas that scarcely reacts with the material gas or the reducing gas is used, and thereby, there can be sufficiently secured a time for removing fluorine from the metal layer 214. This can further reduce failure originated from fluorine.

Fourth Embodiment

A fourth embodiment is hereafter described. In the present embodiment, the additive gas has an effect of reducing the metal contained in the material gas. When the material gas includes tungsten hexafluoride and the reducing gas includes hydrogen, the additive gas exemplarily includes carbon monoxide. When the metal layer 214 is formed using the additive gas including carbon monoxide, the carbon monoxide gas is introduced simultaneously to the hydrogen gas which is the reducing gas. Since this enhances power of reducing tungsten, a cycle rate of the metal layer 214 can be improved.

Moreover, by adjusting an amount of addition of the carbon monoxide gas, carbon can be taken into the metal layer 214 as desired. Therefore, failure originated from fluorine can be reduced while the resistance of the metal layer 214 is reduced.

Fifth Embodiment

A fifth embodiment is hereafter described. In the present embodiment, the additive gas has a property of oxidizing the metal contained in the metal layer 214. When the material gas includes tungsten hexafluoride, the additive gas is exemplarily oxidation gas.

FIG. 8 is a flowchart showing manufacturing steps of the metal layer 214 in the present embodiment. Description of the similar steps to those of the flowchart shown in FIG. 6 is omitted.

As shown in FIG. 8, in the present embodiment, the additive gas is introduced (step S15) after the inert gas introduction step (step S14). After that, the inert gas is introduced again (step S16). When the gas introduction steps as above are repeated, a surface of tungsten formed into a film is oxidized by the additive gas, and hence, the resulting tungsten oxide can be etched when the material gas including tungsten hexafluoride is introduced in the next cycle.

In the present embodiment, by adjusting an amount of introduction of the additive gas (oxidation gas) such that the tungsten oxide can be easily etched (coverage thereof is poor), a frontage of the metal layer 214 (outward opening part thereof) expands in introducing the material gas. This improves a property of embedding tungsten.

Moreover, when the additive gas is oxidation gas, an oxygen concentration in the metal layer 214 is highest at and near the frontage and becomes lower more inward (more on the block insulating film 31 side). Therefore, by adjusting the amount of introduction of the oxidation gas, the property of embedding tungsten can be improved and failure originated from fluorine can be reduced while the resistance of the metal layer 214 is reduced.

While certain embodiments have been described, these embodiments have been presented by way of example only, and are not intended to limit the scope of the inventions. Indeed, the novel embodiments described herein may be embodied in a variety of other forms; furthermore, various omissions, substitutions and changes in the form of the embodiments described herein may be made without departing from the spirit of the inventions. The accompanying claims and their equivalents are intended to cover such forms or modifications as would fall within the scope and spirit of the inventions. 

1. A semiconductor device comprising: a barrier metal layer provided on a surface of an insulating layer; and a conductive layer having a first metal layer provided on a surface of the barrier metal layer, and a second metal layer provided on a surface of the first metal layer, wherein the second metal layer includes an identical metal to metal of the first metal layer, and an impurity configured to remove fluorine bonded to the metal.
 2. The semiconductor device of claim 1, wherein a bond energy between the impurity and the metal is higher than a bond energy between the metal and the fluorine.
 3. The semiconductor device of claim 1, wherein the impurity includes at least one of an aluminum atom (Al), a zirconium atom (Zr), a hafnium atom (Hf), a silicon atom (Si), a boron atom (B), a titanium atom (Ti), an oxygen atom (O), an yttrium atom (Y) and a carbon atom (C).
 4. The semiconductor device of claim 1, wherein a concentration of the impurity is uniform in the second metal layer.
 5. The semiconductor device of claim 1, wherein an impurity concentration in the second metal layer is 1×10¹⁹ to 1×10²¹ atoms/cm³.
 6. The semiconductor device of claim 1, wherein the second metal layer includes at least one high concentration layer in which a concentration of the impurity is locally high.
 7. A manufacturing method of a semiconductor device, comprising: forming a barrier metal layer on a surface of an insulating layer; forming a first metal layer on a surface of the barrier metal layer; and forming, on a surface of the first metal layer, a second metal layer including an identical metal to metal of the first metal layer, and an impurity configured to remove fluorine bonded to the metal.
 8. The manufacturing method of claim 7, wherein a bond energy between the impurity and the metal is higher than a bond energy between the metal and the fluorine.
 9. The manufacturing method of claim 7, wherein the impurity includes at least one of an aluminum atom (Al), a zirconium atom (Zr), a hafnium atom (Hf), a silicon atom (Si), a boron atom (B), a titanium atom (Ti), an oxygen atom (O), an yttrium atom (Y) and a carbon atom (C).
 10. The manufacturing method of claim 7, wherein a concentration of the impurity is uniform in the second metal layer.
 11. The manufacturing method of claim 7, wherein an impurity concentration in the second metal layer is 1×10¹⁹ to 1×10²¹ atoms/cm³.
 12. The manufacturing method of claim 7, comprising forming, in the second metal layer, at least one high concentration layer in which a concentration of the impurity is locally high. 